1. Field of the Invention
The invention relates to a sheet ejection mechanism and a sheet feeding system, and more particularly, to a sheet ejection mechanism in a duplex sheet feeding system and the duplex sheet feeding system.
2. Description of the Prior Art
In general, overlap of feeding edge and trailing edge of a recording medium occurs in a gap between two sheet ejection rollers. Such overlap may easily stop and jam the recording medium during conveying and lower the quality of printing or scanning.
Please refer to FIG. 1A. The U.S. Pat. No. 6,307,614 B1 discloses a method for scanning the recording medium. When the recording medium is scanned with duplex scanning, the feeding edge can not enter the gap formed between a roller 52 and a roller 54, because of the direction of rotation of the two rollers 52, 54, and the recording medium is buckled in front of the gap. Please refer to FIG. 1B. The thrust of the feeding edge of the recording medium overcomes the friction between the recording medium and the rollers so that the rollers 52, 54 are driven to rotate along an opposite direction and convey the recording medium into the gap between the rollers 52, 54.
Such type of design, however, causes problem as follow:
The system reduces its amount of recording medium ejection because the feeding edge of the recording medium, which has done its second side imaging, stops for a while before entering the gap between the two rollers.
In general, the used surface of the recording medium is not smoothly and for the recording medium to enter two tightly adjacent rollers, jamming easily occurs. The recording medium buckles and the quality of output degrades when the recording medium enters the gap formed between two rollers 52, 54.
The upper part of the recording medium and the lower part of the recording medium feed along opposite direction when the recording medium enters the gap formed between two rollers 52, 54. Additionally, the upper part of the recording medium also feeds along opposite direction to the rotation direction of the sheet ejection roller. The upper part of the recording medium has therefore been pulled, which increases overall system torque. The upper part of the recording medium may also be damaged by the pulling force.
To solve the problem mentioned above, please refer to FIG. 1C. The U.S. Pat. No. 6,493,060 B2 discloses a movable driven roller in the sheet ejection mechanism. The gap is formed between two rollers using high power solenoid for overcoming the elasticity of the driven roller before the feeding edge of the recording medium goes to the roller 62 for scanning. The feeding edge of the recording medium can then pass the rollers more smoothly. Such mechanism design, however, uses expensive high power solenoid and needs an additional promotional mechanism for moving the driven roller.
Additionally, the surface of the recording medium produces the mark of the roller engaging by the force of the roller contact. For this reason, the original recording medium is broken by the mark.